Digital television signals of various formats are transmitted from broadcast stations (and may be available from playback devices). Typical digital television signal may be a HD (High Definition) signal having a HD format of 1,125 total number of scanning lines (1,080 effective number of scanning lines) or a SD (Standard Definition) signal having a SD format of 525 total number of scanning lines (effective 480 number of scanning lines).
There are two types of the HD signal; i.e., a S-HD signal and an original HD signal. The S-HD signal has the HD format of 1,125 total number of scanning lines into which broadcast stations have up-converted the SD format of 525 total number of scanning lines. For example, the original HD signal may have the HD format produced from pictures taken by high-definition TV cameras. Japanese Unexamined Patent Publication No. 2004-289753 discloses a technique to distinguish between the S-HD signal and the original HD signal.
According to the above prior art, the picture quality of the S-HD signal and that of the original HD signal are corrected in accordance with their respective characteristics because the frequency bands of the S-HD signal and the original HD signal are different from each other. However, as described in the paragraph 0005 of Japanese Unexamined Patent Publication No. 2004-289753, only the sharpness (contour correction) is considered as an adjustment of picture quality in the prior art. The color-reproduction range of the S-HD signal and that of the original HD signal are different from each other, and a color-reproduction range of the S-HD signal is close to that of NTSC signal. Therefore, different approaches need to be adopted to the color correction, as the adjustment of picture quality, of the S-HD signal and that of the original HD signal. However, such different approaches are not considered in the above prior art.
Also, the above prior art discloses the following teachings for distinguishing between the S-HD signal and the original HD signal:
(i) to use aspect ratio information added to the digital TV signal
(ii) to detect side panels added to right and left sides of picture of the digital TV signal.
In many cases, however, such aspect ratio information is not added to the digital TV signal. In such cases, the prior art fails to distinguish between the S-HD signal and the original HD signal. Besides, the detection of side panels added to right and left sides of the picture of the digital TV signal is based on the assumption that the aspect ratio of the picture is 4:3 as shown in FIG. 2 of this application. In the case of some S-HD signals, however, the aspect ratio of the picture that is 16:9 also exists as shown by the reference numeral 204 in FIG. 2. Even if the aspect ratio of the picture is 4:3, it is difficult to detect side panels if side panels are not black, but have certain brightness as shown by the reference numeral 203 in FIG. 2 or if side panels contain certain picture images. In this case, the picture may be regarded as having the aspect ratio of 16:9. Thus, the above prior art fails to adequately distinguish between the S-HD signal and the original HD signal.
Hence a need exists for providing a technique to distinguish between the S-HD signal and the original HD signal and for providing a technique to carry out an adjustment of picture quality of both the S-HD signal and the original HD signal respectively and appropriately.